Field of the Invention
The present invention relates to a charging device for charging a surface of an image hearing member, such as a photosensitive member, to an image forming apparatus that includes the charging device and that forms an image on a recording medium, and to a process cartridge attached thereto.
Description of the Related Art
In recent years, a contact DC charging technique has been widely used as a charging device in an image forming apparatus, such as an electrophotographic apparatus or electrostatic recording apparatus. The contact DC charging technique uses a conductive charging member, in place of a corona charger, causes the charging member to abut on a photosensitive member, and evenly charges a surface of the photosensitive member, and suppresses ozone generation. One example of that technique is applying a DC bias to a charging roller, which is a charging member, performing evenly discharging while rotating the charging roller in contact with a surface of a photosensitive member, and uniformly charging the surface of the photosensitive member.
The charging roller is required to keep its location in a longitudinal direction constant to properly charge a printing area, and it is recommended that the charging roller be positioned in the longitudinal direction. One example of such a configuration is illustrated in Japanese Patent No. 4749049. The illustrated configuration has a positional relationship between the photosensitive member and charging roller in which the axis of rotation of the photosensitive member and the axis of rotation of the charging roller intersect with each other at a predetermined angle (intersect angle). In that configuration, the charging roller can receive a thrust in the longitudinal direction by being rotated and can be moved to a predetermined location.
Unfortunately, the contact DC charging technique tends to suffer charging failures because the charging roller is in direct contact with the surface of the photosensitive member and thus toner, an external additive, or other additive is apt to be attached to the surface of the charging roller. In particular, if the charging roller has no enhanced longevity or there is no cleaning member for cleaning the surface of the photosensitive member, soiling of the charging roller is a serious problem. Various means for cleaning the charging member to prevent such soling of the surface of the contact charging member have been proposed. One example configuration illustrated in Japanese Patent Laid-Open No. 2002-108069 cleans the contact charging member by using a brush.
There is a method that enables the charging roller and photosensitive member to receive a thrust in a certain direction with respect to the longitudinal direction to position the charging roller and photosensitive member in the longitudinal direction by disposing the photosensitive member and charging roller with the intersect angle formed therebetween, as described above, and, in the case where the charging roller is driven through a gear, by using a helical gear as the gear. With this method, the charging roller and photosensitive member can be moved in a predetermined direction and can be positioned.
However, when the brush member for cleaning the surface of the charging roller abuts on the surface of the charging roller, a load occurs in the charging roller. This hinders smooth movement of the charging roller in the longitudinal direction, and thus the longitudinal locations of the charging roller and photosensitive member are not constant. Although the thrust can be increased by increasing the intersect angle, this state is undesired because it destabilizes the abutment in the longitudinal direction.